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Steps to develop early warning systems and future scenarios of storm wave-driven flooding along coral reef-lined coasts
Tropical coral reef-lined coasts are exposed to storm wave-driven flooding. In the future, flood events during storms are expected to occur more frequently and to be more severe due to sea-level rise, changes in wind and weather patterns, and the deterioration of coral reefs. Hence, disaster managers and coastal planners are in urgent need of decision-support tools. In the short-term, these tools can be applied in Early Warning Systems (EWS) that can help to prepare for and respond to impending storm-driven flood events. In the long-term, future scenarios of flooding events enable coastal communities and managers to plan and implement adequate risk-reduction strategies. Modeling tools that are used in currently available coastal flood EWS and future scenarios have been developed for open-coast sandy shorelines, which have only limited applicability for coral reef-lined shorelines. The tools need to be able to predict local sea levels, offshore waves, as well as their nearshore transformation over the reefs, and translate this information to onshore flood levels. In addition, future scenarios require long-term projections of coral reef growth, reef composition, and shoreline change. To address these challenges, we have formed the UFORiC (Understanding Flooding of Reef-lined Coasts) working group that outlines its perspectives on data and model requirements to develop EWS for storms and scenarios specific to coral reef-lined coastlines. It reviews the state-of-the-art methods that can currently be incorporated in such systems and provides an outlook on future improvements as new data sources and enhanced methods become available.
Aggregated morphodynamic modelling of tidal inlets and estuaries
Aggregation is used to represent the real world in a model at an appropriate level of abstraction. We used the convection-diffusion equation to examine the implications of aggregation progressing from a three-dimensional (3D) spatial description to a model representing a system as a single box that exchanges sediment with the adjacent environment. We highlight how all models depend on some forms of parametric closure, which need to be chosen to suit the scale of aggregation adopted in the model. All such models are therefore aggregated and make use of some empirical relationships to deal with sub-scale processes. One such appropriately aggregated model, the model for the aggregated scale morphological interaction between tidal basin and adjacent coast (ASMITA), is examined in more detail and used to illustrate the insight that this level of aggregation can bring to a problem by considering how tidal inlets and estuaries are impacted by sea level rise.
Deep learning video analysis as measurement technique in physical models
In coastal engineering context, the use of video imagery is widespread. Especially in field settings along sandy coasts, many types of data have been derived from video imagery, often using non-learning analysis techniques. Recent advances in the field of computer vision and deep learning allow for the automation of image segmentation. In this paper, these techniques are combined with video imagery of physical model tests, resulting in an innovative non-intrusive measurement technique. This technique is validated for three different applications: the measurement of surface elevation, wave run-up and bed level development. In addition to demonstrating its potential as an alternative for existing measurement instruments, it is shown that the added detail in the spatial or temporal domain provided by the technique can lead to new insights. Examples of this are the detailed analysis on the variability of the run-up height over the width of the flume and the spatial distribution of run-up velocities over the slope.
Combined effects of physical and biological processes on coastal dynamics and recovery : the BLUEcoast project approach
Poorly constrained uncertainties limit the prediction of medium to long-term regional sediment budgets and morphological change, and thus hinder coastal management decision-making. We present a multi-disciplinary approach that aims to address this challenge and is implemented in the BLUEcoast project. The approach brings together scientists and coastal stakeholders across a range of scientific disciplines. Quantifying all processes at all scales is not feasible and our approach uses targeted representative case studies, which are carefully selected to allow subsequent upscaling and ensure transferability. We illustrate this approach with specific examples from the BLUEcoast consortium.
Earth observation and coastal climate services for small islands
The workshop on Earth Observation and Coastal Climate Services for Small Islands, held in Guadeloupe in November 2019, brought together 35 participants constituting stakeholders predominantly from the Caribbean with representation from the Pacific and Indian Ocean region, as well as providers of climate and earth observation services. The workshop was jointly organized by the Climate Service Center Germany – Helmholtz Zentrum Geesthacht and the University of the French Antilles in Guadeloupe. The aims of the workshop were to: (1) recognize the common challenges and data needs of small islands in relation to risk reduction and climate change adaptation; (2) identify development needs for additional data services; and (3) identify useful methods for the dissemination of such services. The workshop format combined participatory methods, individual presentations, plenary discussions and group work. The presentations highlighted regionally (for the Caribbean) and globally available data sources as well as location specific case studies.
Improved understanding of the link between catchment-scale vegetation accessible storage and satellite-derived Soil Water Index
The spatio‐temporal dynamics of water volumes stored in the unsaturated root‐zone are a key control on the response of terrestrial hydrological systems. Robust, catchment‐scale root‐zone soil moisture estimates are thus critical for reliable predictions of river flow, groundwater recharge or evaporation. Satellites provide estimates of near‐surface soil moisture that can be used to approximate the moisture content in the entire unsaturated root‐zone through the Soil Water Index (SWI). The characteristic time length (T, in days), as only parameter in the SWI approach, characterizes the temporal variability of soil moisture. The factors controlling T are typically assumed to be related to soil properties and climate, however, no clear link has so far been established. In this study, we hypothesize that optimal T values (Topt) are linked to the interplay of precipitation and evaporation during dry periods, thus, to catchment‐scale vegetation‐accessible water storage capacities in the unsaturated root‐zone. We identify Topt by matching modeled time series of root‐zone soil moisture from a calibrated process‐based hydrological model to SWI from several satellite‐based near‐surface soil moisture products in 16 contrasting catchments in the Meuse river basin. Topt values are strongly and positively correlated with vegetation‐accessible water volumes that can be stored in the root‐zone, here estimated for each study catchment both as model calibration parameter and from a water‐balance approach. Differences in Topt across catchments are also explained by land cover (% agriculture), soil texture (% silt) and runoff signatures (flashiness index).
Development and evaluation of flood forecasting models for forecast-based financing using a novel model suitability matrix
As an extension to flood early warning systems, forecast-based financing is a novel financial mechanism that facilitates humanitarian actions prior to anticipated floods by triggering release of pre-allocated funds based on exceedance of forecast thresholds. This paper advocates a stronger interface between model developers and model users in the development of flood forecasting models for forecast-based financing to support upscaling in global disaster risk reduction. Machine learning models of increasing complexity and a state-of-the-art process-based distributed hydrological model are developed and assessed with a holistic and flexible framework for evaluation that allows for incorporation of local contingencies and needs at end-user level. The results demonstrate how this framework can be used to select models with complementary qualities, thereby identifying possible candidates for hybridization and establishing application-oriented grounds for implementation of forecast-based financing. The model suitability matrix can be adjusted and applied on a case-by-case basis through stakeholder approach.
Effect of pre-shearing on the steady and dynamic rheological properties of mud sediments
Mud sediments can exhibit a complex rheological behaviour, particularly a thixotropic character or structural recovery after breakup due to the presence of organic matter/biopolymer. Such biopolymers can lead towards the development of flocculated structures having multiple length scales which are sensitive to shearing rate and history. In this study, the extent and rate of structural recovery of mud sediments was studied by measuring the storage modulus as a function of time using small amplitude oscillatory tests after a destructive steady shearing. This linear viscoelastic response of the sediments was further investigated as a function of several parameters including pre-shear rate, pre-shear time, measuring geometry, mud density and organic matter content. The equilibrium storage modulus (G') and the characteristic time (tr) for the structural recovery of the sediment matrix were estimated by fitting the experimental data to a stretched exponential function. The normalized storage modulus, G'/G'0 (i.e., structural parameter) was used to relate it with the yield stresses of mud sediments. The results showed that the recovery of structure after shearing was instantaneous (tr being of the order of seconds), however, the extent of recovery was highly dependent on the studied parameters. The extent of recovery was higher for the samples with lower density and lower organic matter content. The effect of the shearing time on tr and G' was almost negligible, which implies that the destruction of the structure was achieved within seconds. Using vane geometry, the extent of recovery was higher than using Couette geometry which is linked with the distribution of shear stresses within the cell for each geometry. Yield stresses showed a strong dependency on structural parameter, until it reaches very small values. At low values of structural parameter, the yield stresses were constant as the structural recovery was even faster than the time required to perform the amplitude sweep tests. This study provides an extensive knowledge about the structural recovery in mud sediments under different shearing conditions which can be useful for sediment management.
Advances and practices on the research, prevention and control of land subsidence in coastal cities
Land subsidence severely threatens most of the coastal plains around the world where high productive industrial and agricultural activities and urban centers are concentrated. Coastal subsidence damages infrastructures and exacerbates the effect of the sea-level rise at regional scale. Although it is a well-known process, there is still much more to be improved on the monitoring, mapping and modeling of ground movements, as well as the understanding of controlling mechanisms. The International Geoscience Programme recently approved an international project (IGCP 663) aiming to bring together worldwide researchers to share expertise on subsidence processes typically occurring in coastal areas and cities, including basic research, monitoring and observation, modelling and management. In this paper, we provide the research communities and potential stakeholders with the basic information to join the participating teams in developing this project. Specifically, major advances on coastal subsidence studies and information on well-known and new case studies of land subsidence in China, Italy, The Netherlands, Indonesia, Vietnam and Thailand are highlighted and summarized. Meanwhile, the networking, dissemination, annual meeting and field trip are briefly introduced.
Rapportage NKWK-KBS inventarisatie monitoring lokale klimaatbestendigheid, fase 1
Centrale onderzoeksvraag was: Welke (combinatie van) data vormen een bruikbare indicator voor de lokale en regionale klimaatbestendigheid in de huidige situatie, t.a.v. regen- en grondwateroverlast, droogte en hitte en tweedelaagsveiligheid, en zullen dus wijzigen na uitvoering van adaptatie-maatregelen of andere veranderingen in de omgeving?.